Almost all spark electrodes, from those used in combustion engine spark plugs to gas heater ignitors, have a central metallic conductor housed in a ceramic or glass insulator. A fundamental difficulty with such electrodes has been that the thermal expansion rate of the interior electrode is greater than that of the surrounding ceramic insulator. As such, as the electrode becomes hotter during use and expands, it applies pressure to the inside wall of the insulator. Such ceramic and glass insulators are by their nature extremely brittle, and thus are prone to cracking under thermal expansion pressure from the electrode. A further problem with such prior art devices is that the electrode must be firmly mounted within the housing in such a way that it will not become loose over time. The methods heretofore used for assembling the electrode to the housing are at once expensive and often require more components than just the electrode and ceramic housing.
Several prior art devices are available that reduce the chance of such structural failure and provide unique methods for holding the electrode in place within the ceramic housing. For example, such devices are taught in U.S. Pat. No. 2,267,571 to McDougal on Dec. 23, 1941; U.S. Pat. No. 3,346,760 to Jalbing et al. on Oct. 10, 1967; U.S. Pat. No. 3,229,144 to Poland on Jan. 11, 1966; U.S. Pat. No. 3,134,230 to Lynch on May 26, 1964; and U.S. Pat. No. 3,295,005 to Poellet et al. on Dec. 27, 1966. Such devices typically teach that the electrode is to be fixed to the ceramic housing by braising processes, or by melting the ceramic or glass housing around the electrode and letting the molten glass set the electrode into place. Other prior art devices teach a spark electrode assembly having multiple parts that cooperate to hold the electrode in place. All of these prior art solutions are relatively expensive, and many require more than two parts. As such, the prior art devices tend to be relatively complex, and thus more prone to failure.
Clearly, then, there is a need for a spark electrode device that can be readily assembled and that comprises only the two basic parts of the electrode and the insulating, ceramic housing. Such a needed device would accommodate the thermal expansion of the electrode. Such a needed device would further allow for the thermal contraction of the electrode while still firmly holding the electrode in place within the housing. The present invention fulfills these needs and provides further related advantages.